A chance to hear rarely performed Mozart made for a compelling draw Saturday to the final night of the Mostly Mozart Festival at Avery Fisher Hall.

While the piece was likely new to most ears, though, the obscure cantata “Davidde penitente” (“Penitent David”) was full of familiar material. With text based on psalms of David written by Lorenzo da Ponte — often considered his finest librettist — “Davidde penitente” includes much of the music from the unfinished C-minor Mass, with a few new arias.

“A te, fra tanti affanni,” for tenor, could easily fit into one of the composer’s stronger operas. It begins as a plaintive account of seeking mercy, with winds interjecting and strings pulsing; it then grows robust, buoyant and cheerful as the tenor sings of answered prayers.

Under music director Louis Langrée, the Mostly Mozart Festival Orchestra played with urgency, freshness and brilliant, cohesive sound. At times one wished for more volume and more cutting diction from the Concert Chorale of New York, directed by James Bagwell.

Still, they offered strong, evocative accounts of the penetrating “Sii pur sempre” (“Be ever gracious,” the same music as the Mass’ “Gratias”) and “Se vuoi, puniscimi” (“Punish me, if you will,” the Mass’ “Qui tollis.”) In this context, the latter work’s short repeated string motives resembled striking or flagellating motions, and the sustained vocal line took on a stoic quality.

Less than confident performances from the soloists brought down the overall effect. Soprano Carolyn Sampson sang communicatively, with a lovely sheen in the upper notes of her light, bubbly voice. But her lower range was weaker, and she struggled in her challenging aria.

Mezzo-soprano Sasha Cooke displayed lush, ample tones but seemed a bit awkwardly stretched in music often sung by a soprano. Tenor Steve Davislim sang without the fluidity needed to carry his lyrical part.

It turned out that the more often heard work on the program, the Piano Concerto No. 21, was the more consistently rewarding performance.

British pianist Stephen Hough, Langrée and the orchestra imbued the concerto’s bright outer movements with charm, and the middle section took on an enveloping rhapsodic quality. Hough’s silken legato and vibrant articulation never flagged, even at top speeds.